The evidence on board independence and firm performance has long been mixed—partly because many studies fail to control for ‘two-way causation.’ Struggling companies may be pressured to add independent directors, while successful CEOs often gain influence over board composition. This can create both positive and negative correlations, making simple conclusions unreliable.

However, most studies that attempt to isolate causal channels—such as how board independence affects CEO incentives, risk management, or capital allocation—tend to support a positive impact on profit and value.

Additionally, event-based analysis, comparing company performance before and after key governance shifts (such as CEO replacements, regulatory changes, or competitive shocks), also suggest that firms with strong independent boards tend to navigate disruptions more effectively.

The key question now is whether this remains a meaningful distinction.

Modern NYSE and Nasdaq rules already require a majority of independent directors.

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Using Disclosure Assistant, we ran a quick S&P 500 assessment and found that board independence averages 85%, with most firms falling between 65% and 100%. Variance still exists, but independence levels tend to be concentrated now above the regulatory threshold.
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What remains less explored is whether 'more is always better'. Does increasing independence beyond the 50–60% range offer marginal gains, or does it reach a plateau?

Some studies suggest that while board independence improves oversight, its impact levels off beyond a certain point—where factors like director expertise, engagement, and work load become more important. Other research even suggests potential downsides to excessive independence, such as reduced firm-specific knowledge and an over-reliance on management for information.

For investors, this means board independence isn’t likely to be a simple factor investing signal on its own, though outliers — such as unusually low levels relative to peers— could still be useful governance flags. A company hovering at the bare minimum may warrant further research into board structure, director backgrounds, and governance effectiveness.

Of course, board composition is just one element of governance analysis. And other factor-relevant areas — such as resource efficiency, human capital and investment — also play bigger roles in long-term performance.

Disclosure Assistant can help investors explore alternative factor investing strategies or ESG-enhanced smart beta approaches by extracting key data, identifying proxies, or collating qualitative assessments when direct metrics are unavailable.

Sources:

Responsible Capital analysis of S&P500 documents and disclosures

A Survey of Recent Evidence on Boards of Directors and CEO Incentives (Masulis, 2020)

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